The present invention relates to a head gasket to be attached between two members, such as a cylinder head and a cylinder block, of an internal combustion engine, more specifically, a cylinder head gasket for a multi-cylinder semi-closed engine having a plurality of water holes and a gas releasing portion.
A cylinder head gasket to be applied to an engine for a vehicle includes a plurality of cylinder bores, water holes, oil holes, bolt holes and the like according to its use, and the holes to be sealed are provided with various sealing devices.
While the cylinder head gasket is manufactured according to a shape of a cylinder block, the cylinder block is classified into an open deck type cylinder block, a closed deck type cylinder block and a semi-closed deck type cylinder block according to a shape of a water jacket for cooling the cylinders.
The open deck type cylinder block includes openings for cooling water paths connected to a water jacket provided around each cylinder bore on a joining surface with a cylinder head. Thus, the open deck type cylinder block has a good cooling ability, can be made compact and easily manufactured.
On the other hand, the closed deck type cylinder block does not include the cooling water paths around the respective cylinder bores on the joining surface with the cylinder head, and the water jacket is closed on the joining surface of the cylinder block portion. Since the closed deck type cylinder block does not have openings, it is suitable for a high power engine because it has a high rigidity and less deformation. However, since there are no openings, its manufacture and processing are very complicated, which results in a high manufacturing cost.
In the semi-closed deck type cylinder block, an opening portion of the water jacket is partially closed, more specifically, an upper portion of the water jacket around the cylinder bore is partially closed in a circumferential direction of the cylinder bore to thereby obtain a rigidity of a cylinder. Also, since the semi-closed deck type cylinder block has openings for the cooling water paths connected to the water jacket, it has a good cooling ability and can be manufactured easily.
The cylinder head gasket of the present invention is used for the semi-closed deck type engine. In this engine, as shown in FIG. 5, water holes 33 as the openings for the cooling water paths connected to the water jacket are formed on both sides of the respective cylinder bores 32 in a circular arc shape on a joining surface 31 with the cylinder head on a side of the cylinder block 30 so as to intermittently surround the respective cylinder bores 32.
Therefore, as shown in FIG. 6, in a cylinder head gasket 40, water holes 43 in a shape of a circular arc are intermittently disposed around the respective cylinder bores 42 provided on a gasket plate 41. Sealing devices 52, 53, 55 are provided; around the cylinder bores 42, water holes 43 and oil holes 45 and the like to thereby obtain the respective sealing abilities.
However, when the engine is operated, a combustion gas having high pressure and temperature is generated in the cylinder bores and may damage cylinder bore sealing devices 52 formed of beads or the like provided around the cylinder bores 42. Further, since the engine vibrates, the cylinder head gasket 40 is repeatedly subjected to various deformations. Thus, the combustion gas may leak, in an extremely small amount, through the cylinder bore sealing devices 52 from the cylinder bores 42.
In case the combustion gas leaks, there is no gas releasing portion. Moreover, when the sealing ability of the water hole sealing devices 53 for the water holes 43 becomes insufficient due to their deterioration, the leaked gas flows into the water jacket through the water holes 43 to thereby cause a gas accumulation.
The gas accumulation may be very small, but the cooling water can not pass through the gas accumulated portion to cause a flow prevention by gas. As a result of the flow prevention by gas, a circulation of cooling water is limited and, in the worst case, an overheat may take place.
Also, in case the extremely small amount of the combustion gas leaks outside the gasket 40 from the cylinder bores 42 and contacts machineries of the engine itself and other parts around the engine, functions of the machineries and other parts may be deteriorated. Therefore, it is necessary to prevent the leaked gas from contacting the machineries and other parts. In the conventional gasket, it has been impossible to find out portions where the gas leaks.
In this respect, in Japanese Patent Publication (KOKAI) No. 11-108189, a plate for forming a gasket includes a bead surrounding an outer area of the gasket, wherein a part of the plate including the bead is notched to allow a leaked gas to escape therethrough. However, the leaked gas is not smoothly lead outside the gasket and may enter again into water or other holes.
Also, it is known to surround a water hole by a bead to seal therearound, which is disclosed in, such as Japanese Patent Publications No. 11-22827, No. 9-166218, No. 8-291865 and No. 7-229564. In these cases, the water hole or holes are simply surrounded by the bead for sealing.
In view of the above problems, the present invention has been made, and an object of the invention is to provide a cylinder head gasket to be applied to a semi-closed deck type engine, wherein gas leaked from cylinder bore sealing devices is guided outside the cylinder head gasket through a gas releasing portion so that even if the gas leaks from the cylinder bore sealing devices, the leaked gas is prevented from entering water holes.
Another object of the invention is to provide a cylinder head gasket as stated above, wherein the leaked gas is guided to one end side or both end sides of the cylinder head gasket in a longitudinal direction so that the leaked gas does not damage other machinery or device.
A still further object of the invention is to provide a cylinder head gasket as stated above, wherein a strength of a part of a water hole sealing device located on a side of the cylinder bore, i.e. on a side where the water hole sealing device is likely to contact the leaked combustion gas and to receive a high pressure, is formed stronger than that of a part of the water hole sealing device located outside the water holes, so that a sealing surface pressure can be made high to further prevent the leaked gas from entering into the water holes.
Further objects and advantages of the invention will be apparent from the following description of the invention.
A cylinder head gasket of the invention is used for a multi-cylinder semi-closed deck type engine, wherein a series of water holes are disposed around a plurality of cylinder bores. Cylinder bore sealing devices surround the cylinder bores to seal therearound.
According to a first aspect of the invention, a water hole sealing device is formed to seal a series of water holes disposed around the cylinder bore sealing devices by surrounding the same, and the water hole sealing device includes a gas releasing portion at a side of the cylinder bore sealing devices to communicate with an outside of the gasket to thereby release a gas slightly leaked from the cylinder bore sealing devices to an outside.
According to a second aspect of the invention, a series of water holes disposed around a plurality of cylinder bore sealing devices are divided into two groups. Each group of the water holes is surrounded by a first water hole sealing device, and a second water hole sealing device, respectively, So that two gas releasing portions are provided at both sides of the cylinder bore sealing devices. Thus, an inner side of the water hole sealing device communicates with an outside of the gasket, and the combustion gas slightly leaked from the cylinder bore sealing devices is released through the two gas releasing portions.
More specifically, one or two water hole sealing devices surround a plurality of the water holes to seal the same, and also, a cylinder bore side portion of the water hole sealing device is allowed to function as a guiding path of the combustion gas slightly leaked from the cylinder bore sealing devices, so that the leaked combustion gas is released outside the gasket through the gas releasing portion or portions of the water hole sealing device or devices.
Therefore, since the combustion gas slightly leaked from the cylinder bore sealing devices can be guided along the water hole sealing device or devices on the cylinder bore side to discharge the gas through the gas releasing portion or portions, the leaked combustion gas is prevented from flowing into a cooling water in a water jacket through the water holes by passing the water hole sealing device or devices.
According to a third aspect of the invention, in the cylinder head gasket, the gas releasing portion is disposed on an end side of the cylinder head gasket in the longitudinal direction.
More specifically, in case the two, i.e. first and second, water hole sealing devices are used, the two water hole sealing devices are disposed on both sides of a line connecting centers of the respective cylinder bores of the cylinder head gasket. The first water hole sealing device continuously seals the water holes disposed on one side of the cylinder bores, and the second water hole sealing device continuously seals the water holes disposed on the other side of the cylinder bores.
Since the leaked gas is guided to both end sides of the cylinder head gasket in the longitudinal direction, influence of the leaked gas can be reduced. Also, when the cylinder head is tightened by bolts, since tightening pressures on both end sides of the cylinder head gasket in the longitudinal direction are not so strong, the end sides are suitable as the gas releasing paths.
According to a fourth aspect of the invention, in the cylinder head gasket, the water hole sealing device is formed of a half bead or a full bead.
The water hole sealing device may be formed of a known device, but the water hole sealing device can be easily formed of a bead. Although a space between the water hole and the cylinder bore is narrow, it is necessary to provide the cylinder bore sealing device and the water hole sealing device therein. Thus, it is preferable that the water hole sealing device is formed of a half bead.
According to a fifth aspect of the invention, in the cylinder head gasket, a strength of a bead as the water hole sealing device on a side of the cylinder bore is made stronger than that of a bead outside the water hole.
Thus, the strength of the bead on the side subjected to the high temperature combustion gas and high pressure is made strong and a high surface pressure can be held to thereby effectively guide the leaked gas outside.
The strength of the bead can be easily varied by changing a width or height of the bead.